Many biological fluid processing protocols include filtering the fluid before use. For example, a biological fluid such as blood or at least one blood component can be filtered to remove undesirable material such as debris, gels, microaggregates and/or leukocytes before transfusing the biological fluid. In some protocols, for example, involving bedside administration of blood or blood components, two or more units of blood components such as red blood cells or platelet concentrate can be leukocyte depleted and administered.
However, some of these protocols have suffered from a number of drawbacks. For example, some filters have suffered from clogging, which can prevent or delay the administration of the desired number of units. Alternatively, the use of a separate filter for each unit of blood or blood component can be time consuming, since each filter has to be attached to the blood processing system, and primed. Additionally, some fluid remains in each filter after filtration, and is not transfused to the patient. Thus, the cumulative loss of this held up fluid can be significant.
In an attempt to overcome the problem of clogging, some filter devices include two filter elements, separated by a partition plate, in a single housing. The elements are pressed against the opposite sides of the partition plate, and the elements can be sealed to the opposing sides of the plate. In typical use, blood enters the top of the device, and contacts the partition plate. The blood is then directed to, and passes through, a filter element. The filtered blood subsequently exists the bottom of the device.
These filter devices have also suffered from a number of problems, particularly with respect to difficulty in priming. Air can be trapped in the device, making it difficult to wet either or both of the filter elements. As a result, it may be difficult to pass blood through the device, or blood may flow through one of the filter elements, and little or no blood flows through the other element. Also, since air is trapped, it can be difficult to efficiently drain the device. Additionally, or alternatively, since the device must be of sufficient size to accommodate two filter elements, the device may retain an undesirably large amount of the valuable blood or blood component.
Another disadvantage of at least some of these filters, e.g., those used with one unit of blood, is that they are difficult to include in a centrifugable blood bag system. For example, the filter may be too large to fit in a centrifuge cup, and/or the filter or blood bags may be damaged during centrifugation.
The present invention provides for ameliorating at least some of the disadvantages of the prior art. These and other advantages of the present invention will be apparent from the description as set forth below.